Series vs. Parallel Battery Operations

Understanding the difference between operating batteries in series and parallel is the first step to building the most effective battery system for your application. Being able to run Astro Lithium batteries in either series or parallel mode allows for greater flexibility and increased applications for your systems.

Connecting Batteries in Series

When you operate a battery in series, that means you are connecting two or more batteries together to increase the overall battery systems voltage. It is important to note that this does not increase the capacity of the battery.

To run batteries in series, the negative terminal of one battery is connected to the positive terminal of the next battery. This is repeated for each battery in the series. To complete the series to the source we are trying to power, such as a trolling motor or a golf cart, we would then connect the positive terminal of the first battery and the negative terminal of the last battery to our input source.

If we take two 12 volt batteries of equal amp hour rating and connect them in series, the result will be a 24 volt output with the same amp hour rating. The diagram below shows two Astro Lithium 12V 100Ah batteries in series to power a 24 volt system.

Up to four 12 volt Astro Lithium batteries can be run in series to create a total output voltage of 48 volts. In the next figure we show three batteries in series to create 36 volts.

There are many reasons to operate batteries in series, but they all stem from needing higher output voltage. One example would be to power a 36 volt trolling motor. While Astro Lithium does sell 36 volt batteries, some customers prefer the flexibility of using multiple 12 volt batteries.

CHARGING BATTERIES IN SERIES

To charge batteries in series, use a charger that matches the total combined voltage of all the batteries. Hook up the charger in the same method that the output is wired to, i.e., the positive terminal to the first battery in the series and the negative terminal to the last battery in the series. See the figure below.

NOTE: When connecting batteries in series, the voltage and the amp hour rating (Ah) must be the same for all the batteries in the series.

Connecting Batteries in Parallel

When operating batteries in parallel, we are connecting two or more batteries to increase the battery capacity, also known as amp hour. In this process, the voltage remains the same.

To connect batteries in parallel, the negative terminal of one battery will be connected to the negative terminal of the next battery. This process is repeated for the positive terminals to positive terminals also. You can connect up to six Astro Lithium batteries in parallel with one another.

To hook your parallel connected batteries to you input source, simply use the positive and negative terminals of the first battery in the parallel system.

In the example below, we have two 12V 100Ah batteries connected in parallel to create 200Ah’s of capacity, but still at 12 volts.

The main reason to connect batteries in parallel is to increase capacity. The largest single amp hour rated batteries we have at Astro Lithium are 100Ah. For some applications that may not be enough. For example, for someone who wants to power their camper off-grid for multiple days at a time it may be necessary to run several of these batteries together in parallel to increase overall capacity.

CHARGING BATTERIES IN PARALLEL

Charging batteries properly in parallel is very important to avoid unbalanced cells. To charge batteries correctly in parallel, simply connect your charger to the positive terminal of the first battery and negative terminal of the last battery in the parallel system. You must use a charger that is rated for the same voltage as the individual batteries. See the figure below.

NOTE: When connecting batteries in parallel, the voltage and the amp hour rating (Ah) must be the same for all the batteries in the series.